Crop scientists have been pushing up corn yields for decades. But the newer strains just can't stand the heat

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November 14, 2009 3:01AM (UTC)

A troubling fact about corn: In the United States from 1940-1960, after the introduction of hybrid corn and in the wake of the disastrous Dust Bowl years of 1934 and 1936, corn yields and corn heat tolerance both grew. But since 1960, while yields have continued to grow as new hybrid and genetically modified varieties have been introduced, along with other agricultural innovations, heat tolerance has actually fallen.

Why is this significant? Because after a certain temperature, usually around 86 degrees Fahrenheit, corn yields drop dramatically. And even the most conservative mainstream climate scientist predictions about the effect of global warming include temperature rises that would hammer the corn-growing heartland of the United States.

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These insights come from a fascinating new paper, "The Evolution of Heat Tolerance of Corn: Implications for Climate Change" by North Carolina State University's Michael J. Roberts, a professor of Agricultural and Resource Economics, and Wolfram Schlenker, an economist at Columbia University. The researchers take advantage of a 100 years of incredibly detailed information on corn yields and temperature records in Indiana, the third-largest corn-growing state in the U.S.

Since the mildest scenario for climate change would result in heat extremes "worse than the worst of the Dust Bowl years" the question of corn heat tolerance is critical for the future of the American corn belt. Perhaps most alarming:

The... decline in heat tolerance might be due to the fact that maximizing corn plants for average yields also makes them more sensitive to suboptimal growing conditions..."

Which leads to the question "whether recent increases in yields could only be achieved by making plants less heat resistant, or whether future breeding cycles can increase both heat tolerance and average yields at the same time."

Monsanto, I am sure, would answer the latter part of that question with a resounding affirmative. But the alternative is chilling: We have been progressively breeding and engineering crop strains that are less and less able to cope with climate change.

Roberts and Schlenker conclude with an interesting point about crop prices and income inequality, and a slight dig at Michael Pollan. Pollan has argued for years that subsidizing corn production has led to artificially low prices for corn products and thus contributed to undesirable things such as the obesity crisis. In that scenario, higher prices for corn would be better for our health.

But Roberts And Schlenker point out that such would only be true in a world without vast disparities in income. Rich people, or rich countries like the United States, shrug off rising grain prices and continue to merrily go about their carnivorous corn-fed-meat-eating ways. But poor people in poorer countries can't handle even minor price increases, and starve.

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If incomes were not so divergent, prices would simply rise until enough people substituted to a presumably more healthy diet with less meat. The main reason climate change impacts on agriculture pose such a great threat lies not just in the size of potential production impacts, but also because massive income inequality limits potential adaptation on the demand side of the market. The greatest hope is an uncertain one: that technological change will obviate the need for behavioral change.